Throw Checked Exceptions Like Runtime Exceptions in Java
Throw Checked Exceptions Like Runtime Exceptions in Java
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How to throw a checked exception without catch block or throws clause in Java? Simple!
public class Test {
// No throws clause here
public static void main(String[] args) {
doThrow(new SQLException());
}
static void doThrow(Exception e) {
Test.<RuntimeException> doThrow0(e);
}
@SuppressWarnings("unchecked")
static <E extends Exception> void doThrow0(Exception e) throws E {
throw (E) e;
}
}
Due to generic type erasure, the compiler will compile something here that really shouldn’t compile. Crazy? Yes. Scary? Definitely!
The generated bytecode for doThrow() and doThrow0() can be seen here:
// Method descriptor #22 (Ljava/lang/Exception;)V
// Stack: 1, Locals: 1
static void doThrow(java.lang.Exception e);
0 aload_0 [e]
1 invokestatic Test.doThrow0(java.lang.Exception) : void [25]
4 return
Line numbers:
[pc: 0, line: 11]
[pc: 4, line: 12]
Local variable table:
[pc: 0, pc: 5] local: e index: 0 type: java.lang.Exception
// Method descriptor #22 (Ljava/lang/Exception;)V
// Signature: <E:Ljava/lang/Exception;>(Ljava/lang/Exception;)V^TE;
// Stack: 1, Locals: 1
static void doThrow0(java.lang.Exception e) throws java.lang.Exception;
0 aload_0 [e]
1 athrow
Line numbers:
[pc: 0, line: 16]
Local variable table:
[pc: 0, pc: 2] local: e index: 0 type: java.lang.Exception
As can be seen, the JVM doesn't seem to have a problem with the checked exception thrown from doThrow0(). In other words, checked and unchecked exceptions are mere syntactic sugar
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